The safety belt device in a motor vehicle can be, for example, a lap belt as well as a shoulder belt that runs diagonally across the chest of the vehicle occupant. When the safety belt has been fastened, the lap belt is anchored onto the vehicle frame via two laterally opposing, lower attachment points. Normally, the inner buckling point situated in the crosswise direction of the vehicle is configured to be detachable, namely, with a belt fitting that is provided on the lap belt and whose insertion tongue can be inserted into a belt buckle anchored on the frame side.
German patent application DE 42 15 384 A1 describes a generic belt fitting with a base section and an adjoining insertion tongue. In the base section, there is a belt slit through which a belt strap passes. When the safety belt has been fastened, the belt slit subdivides the belt strap into a lap belt section and a shoulder belt section. In order to block the lap belt section of the safety belt in case of a collision, there is a clamping element that can be adjusted between a release position, in which the belt strap can move freely as it passes through the belt slit, and a clamping position, in which the belt strap is clamped tightly with a clamping force between the clamping element and a clamping stop that functions as a counterbearing. The clamping element can be pivoted around an axis of rotation between the release position and the clamping position, and it is elastically pre-tensioned in the direction of the release position. Consequently, during normal driving, the belt strap can move freely over the running surface of the clamping element. In contrast, in case of a collision, elevated belt forces act upon the clamping element. As a result, the clamping element is moved in a direction of rotation until it reaches the clamping position in which the belt strap is tightly clamped by the clamping force between the clamping element and the clamping stop.
In the state of the art, the clamping element has a clamping crossbar that runs in the crosswise direction of the belt strap. In the clamping position, the clamping crossbar is in linear contact with the belt strap, namely, continuously between the two outer edges of the belt strap in the crosswise direction of the belt strap. This results in a linear, uniform and constant clamping force distribution between the two outer edges of the belt strap over the crosswise direction of the belt strap.
In dynamic safety tests, it was found that, in case of a collision, an excessively high stress can be exerted on the fabric of the belt strap that is clamped tightly between the clamping element and the clamping stop, thus entailing the risk that the belt strap will tear.